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8-3. Alarm Action Diagrams
The followings are diagrams showing alarm actions that can be selected as event 1 and event 2.
8-4. P.I.D.
(1) P (Proportional band)
A percentage at which control output varies with respect to a measuring range is set. Control output increases or
decreases in proportion to a difference between PV and SV values.
The narrower the proportional band, the more conspicuously output changes to strengthen proportional action. If it is
too narrow, however, the result of control will be close to ON-OFF action.
(2) I (Integral time)
This is the function to correct an offset (constant deviation). The longer the integral time, the weaker the corrective
action and the shorter the time the stronger the action but control result may be undulated due to integral hunting.
(3) D (Derivative time)
This is the function to estimate a change in control output, suppress overshoot caused by integration and improve
control stability.
The longer the derivative time, the stronger the derivative action but control result may be vibratile.
(4) MR (Manual Reset)
In PID action, an offset is corrected automatically by I, i.e., integration. When OFF is set for I, correction is not carried
out and so output should be increased or decreased manually. This method is called manual reset.
8-5. Lower Limit and Higher Limit Setting Limiters
ۑ
1
Output limiter means to limit a minimum or maximum value of control output and this function is effective in
specifying the lowest temperature or suppressing overshooting of control.
ۑ
2
Output limiter gives preference to a lower limit value. When a larger lower limit value than a higher limit value is
set, the higher limit value is automatically changed to the lower limit value + 1%. In other words, it is not possible
to set a higher limit value which is less than a lower limit + 1%.
: SV value : Alarm action point
Hysteresis
Action ON
Action ON
Action ON
Action ON
Action ON
Hysteresis
Action ON
PV value
10%
110%
: Scaleover
: Higher limit deviation alarm
: Lower limit deviation alarm
: Within higher/lower limit deviations alarm
: Outside higher/lower limit deviations alarm
: Higher limit absolute value alarm
: Lower limit absolute value alarm
Action ON Action ON Action ON
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